class Schema

class Schema extends DatabaseSchema {
    
    /**
     * A cache of information about blob columns and sequences of tables.
     *
     * This is collected by Schema::queryTableInformation(), by introspecting the
     * database.
     *
     * @see \Drupal\pgsql\Driver\Database\pgsql\Schema::queryTableInformation()
     * @var array
     */
    protected $tableInformation = [];
    
    /**
     * The maximum allowed length for index, primary key and constraint names.
     *
     * Value will usually be set to a 63 chars limit but PostgreSQL allows
     * to higher this value before compiling, so we need to check for that.
     *
     * @var int
     */
    protected $maxIdentifierLength;
    
    /**
     * PostgreSQL's temporary namespace name.
     *
     * @var string
     */
    protected $tempNamespaceName;
    
    /**
     * Make sure to limit identifiers according to PostgreSQL compiled in length.
     *
     * PostgreSQL allows in standard configuration identifiers no longer than 63
     * chars for table/relation names, indexes, primary keys, and constraints. So
     * we map all identifiers that are too long to drupal_base64hash_tag, where
     * tag is one of:
     *   - idx for indexes
     *   - key for constraints
     *   - pkey for primary keys
     *   - seq for sequences
     *
     * @param string $table_identifier_part
     *   The first argument used to build the identifier string. This usually
     *   refers to a table/relation name.
     * @param string $column_identifier_part
     *   The second argument used to build the identifier string. This usually
     *   refers to one or more column names.
     * @param string $tag
     *   The identifier tag. It can be one of 'idx', 'key', 'pkey' or 'seq'.
     * @param string $separator
     *   (optional) The separator used to glue together the aforementioned
     *   identifier parts. Defaults to '__'.
     *
     * @return string
     *   The index/constraint/pkey identifier.
     */
    protected function ensureIdentifiersLength($table_identifier_part, $column_identifier_part, $tag, $separator = '__') {
        $info = $this->getPrefixInfo($table_identifier_part);
        $table_identifier_part = $info['table'];
        $identifierName = implode($separator, [
            $table_identifier_part,
            $column_identifier_part,
            $tag,
        ]);
        // Retrieve the max identifier length which is usually 63 characters
        // but can be altered before PostgreSQL is compiled so we need to check.
        if (empty($this->maxIdentifierLength)) {
            $this->maxIdentifierLength = $this->connection
                ->query("SHOW max_identifier_length")
                ->fetchField();
        }
        if (strlen($identifierName) > $this->maxIdentifierLength) {
            $saveIdentifier = '"drupal_' . $this->hashBase64($identifierName) . '_' . $tag . '"';
        }
        else {
            $saveIdentifier = $identifierName;
        }
        return $saveIdentifier;
    }
    
    /**
     * Fetch the list of blobs and sequences used on a table.
     *
     * We introspect the database to collect the information required by insert
     * and update queries.
     *
     * @param string $table
     *   The non-prefixed name of the table.
     *
     * @return mixed|object
     *   An object with two member variables:
     *   - 'blob_fields' that lists all the blob fields in the table.
     *   - 'sequences' that lists the sequences used in that table.
     *
     * @throws \Exception
     *   Exception thrown when the query for the table information fails.
     */
    public function queryTableInformation($table) {
        // Generate a key to reference this table's information on.
        $key = $this->connection
            ->prefixTables('{' . $table . '}');
        // Take into account that temporary tables are stored in a different schema.
        // \Drupal\Core\Database\Connection::generateTemporaryTableName() sets the
        // 'db_temporary_' prefix to all temporary tables.
        if (strpos($key, '.') === FALSE && strpos($table, 'db_temporary_') === FALSE) {
            $key = 'public.' . $key;
        }
        else {
            $key = $this->getTempNamespaceName() . '.' . $key;
        }
        if (!isset($this->tableInformation[$key])) {
            $table_information = (object) [
                'blob_fields' => [],
                'sequences' => [],
            ];
            $this->connection
                ->addSavepoint();
            try {
                // The bytea columns and sequences for a table can be found in
                // pg_attribute, which is significantly faster than querying the
                // information_schema. The data type of a field can be found by lookup
                // of the attribute ID, and the default value must be extracted from the
                // node tree for the attribute definition instead of the historical
                // human-readable column, adsrc.
                $sql = <<<'EOD'
SELECT pg_attribute.attname AS column_name, format_type(pg_attribute.atttypid, pg_attribute.atttypmod) AS data_type, pg_get_expr(pg_attrdef.adbin, pg_attribute.attrelid) AS column_default
FROM pg_attribute
LEFT JOIN pg_attrdef ON pg_attrdef.adrelid = pg_attribute.attrelid AND pg_attrdef.adnum = pg_attribute.attnum
WHERE pg_attribute.attnum > 0
AND NOT pg_attribute.attisdropped
AND pg_attribute.attrelid = :key::regclass
AND (format_type(pg_attribute.atttypid, pg_attribute.atttypmod) = 'bytea'
OR pg_get_expr(pg_attrdef.adbin, pg_attribute.attrelid) LIKE 'nextval%')
EOD;
                $result = $this->connection
                    ->query($sql, [
                    ':key' => $key,
                ]);
            } catch (\Exception $e) {
                $this->connection
                    ->rollbackSavepoint();
                throw $e;
            }
            $this->connection
                ->releaseSavepoint();
            // If the table information does not yet exist in the PostgreSQL
            // metadata, then return the default table information here, so that it
            // will not be cached.
            if (empty($result)) {
                return $table_information;
            }
            foreach ($result as $column) {
                if ($column->data_type == 'bytea') {
                    $table_information->blob_fields[$column->column_name] = TRUE;
                }
                elseif (preg_match("/nextval\\('([^']+)'/", $column->column_default, $matches)) {
                    // We must know of any sequences in the table structure to help us
                    // return the last insert id. If there is more than 1 sequences the
                    // first one (index 0 of the sequences array) will be used.
                    $table_information->sequences[] = $matches[1];
                    $table_information->serial_fields[] = $column->column_name;
                }
            }
            $this->tableInformation[$key] = $table_information;
        }
        return $this->tableInformation[$key];
    }
    
    /**
     * Gets PostgreSQL's temporary namespace name.
     *
     * @return string
     *   PostgreSQL's temporary namespace name.
     */
    protected function getTempNamespaceName() {
        if (!isset($this->tempNamespaceName)) {
            $this->tempNamespaceName = $this->connection
                ->query('SELECT nspname FROM pg_namespace WHERE oid = pg_my_temp_schema()')
                ->fetchField();
        }
        return $this->tempNamespaceName;
    }
    
    /**
     * Resets information about table blobs, sequences and serial fields.
     *
     * @param $table
     *   The non-prefixed name of the table.
     */
    protected function resetTableInformation($table) {
        $key = $this->connection
            ->prefixTables('{' . $table . '}');
        if (strpos($key, '.') === FALSE) {
            $key = 'public.' . $key;
        }
        unset($this->tableInformation[$key]);
    }
    
    /**
     * Fetches the list of constraints used on a field.
     *
     * We introspect the database to collect the information required by field
     * alteration.
     *
     * @param string $table
     *   The non-prefixed name of the table.
     * @param string $field
     *   The name of the field.
     * @param string $constraint_type
     *   (optional) The type of the constraint. This can be one of the following:
     *   - c: check constraint;
     *   - f: foreign key constraint;
     *   - p: primary key constraint;
     *   - u: unique constraint;
     *   - t: constraint trigger;
     *   - x: exclusion constraint.
     *   Defaults to 'c' for a CHECK constraint.
     *   @see https://www.postgresql.org/docs/current/catalog-pg-constraint.html
     *
     * @return array
     *   An array containing all the constraint names for the field.
     *
     * @throws \Exception
     *   Exception thrown when the query for the table information fails.
     */
    public function queryFieldInformation($table, $field, $constraint_type = 'c') {
        assert(in_array($constraint_type, [
            'c',
            'f',
            'p',
            'u',
            't',
            'x',
        ]));
        $prefixInfo = $this->getPrefixInfo($table, TRUE);
        // Split the key into schema and table for querying.
        $schema = $prefixInfo['schema'];
        $table_name = $prefixInfo['table'];
        $this->connection
            ->addSavepoint();
        try {
            $checks = $this->connection
                ->query("SELECT conname FROM pg_class cl INNER JOIN pg_constraint co ON co.conrelid = cl.oid INNER JOIN pg_attribute attr ON attr.attrelid = cl.oid AND attr.attnum = ANY (co.conkey) INNER JOIN pg_namespace ns ON cl.relnamespace = ns.oid WHERE co.contype = :constraint_type AND ns.nspname = :schema AND cl.relname = :table AND attr.attname = :column", [
                ':constraint_type' => $constraint_type,
                ':schema' => $schema,
                ':table' => $table_name,
                ':column' => $field,
            ]);
        } catch (\Exception $e) {
            $this->connection
                ->rollbackSavepoint();
            throw $e;
        }
        $this->connection
            ->releaseSavepoint();
        $field_information = $checks->fetchCol();
        return $field_information;
    }
    
    /**
     * Generate SQL to create a new table from a Drupal schema definition.
     *
     * @param string $name
     *   The name of the table to create.
     * @param array $table
     *   A Schema API table definition array.
     *
     * @return array
     *   An array of SQL statements to create the table.
     */
    protected function createTableSql($name, $table) {
        $sql_fields = [];
        foreach ($table['fields'] as $field_name => $field) {
            $sql_fields[] = $this->createFieldSql($field_name, $this->processField($field));
        }
        $sql_keys = [];
        if (!empty($table['primary key']) && is_array($table['primary key'])) {
            $this->ensureNotNullPrimaryKey($table['primary key'], $table['fields']);
            $sql_keys[] = 'CONSTRAINT ' . $this->ensureIdentifiersLength($name, '', 'pkey') . ' PRIMARY KEY (' . $this->createPrimaryKeySql($table['primary key']) . ')';
        }
        if (isset($table['unique keys']) && is_array($table['unique keys'])) {
            foreach ($table['unique keys'] as $key_name => $key) {
                $sql_keys[] = 'CONSTRAINT ' . $this->ensureIdentifiersLength($name, $key_name, 'key') . ' UNIQUE (' . implode(', ', $key) . ')';
            }
        }
        $sql = "CREATE TABLE {" . $name . "} (\n\t";
        $sql .= implode(",\n\t", $sql_fields);
        if (count($sql_keys) > 0) {
            $sql .= ",\n\t";
        }
        $sql .= implode(",\n\t", $sql_keys);
        $sql .= "\n)";
        $statements[] = $sql;
        if (isset($table['indexes']) && is_array($table['indexes'])) {
            foreach ($table['indexes'] as $key_name => $key) {
                $statements[] = $this->_createIndexSql($name, $key_name, $key);
            }
        }
        // Add table comment.
        if (!empty($table['description'])) {
            $statements[] = 'COMMENT ON TABLE {' . $name . '} IS ' . $this->prepareComment($table['description']);
        }
        // Add column comments.
        foreach ($table['fields'] as $field_name => $field) {
            if (!empty($field['description'])) {
                $statements[] = 'COMMENT ON COLUMN {' . $name . '}.' . $field_name . ' IS ' . $this->prepareComment($field['description']);
            }
        }
        return $statements;
    }
    
    /**
     * Creates a safe SQL string for a field for table creation or alteration.
     *
     * @param $name
     *   Name of the field.
     * @param $spec
     *   The field specification, as per the schema data structure format.
     */
    protected function createFieldSql($name, $spec) {
        // The PostgreSQL server converts names into lowercase, unless quoted.
        $sql = '"' . $name . '" ' . $spec['pgsql_type'];
        if (isset($spec['type']) && $spec['type'] == 'serial') {
            unset($spec['not null']);
        }
        if (in_array($spec['pgsql_type'], [
            'varchar',
            'character',
        ]) && isset($spec['length'])) {
            $sql .= '(' . $spec['length'] . ')';
        }
        elseif (isset($spec['precision']) && isset($spec['scale'])) {
            $sql .= '(' . $spec['precision'] . ', ' . $spec['scale'] . ')';
        }
        if (!empty($spec['unsigned'])) {
            $sql .= " CHECK ({$name} >= 0)";
        }
        if (isset($spec['not null'])) {
            if ($spec['not null']) {
                $sql .= ' NOT NULL';
            }
            else {
                $sql .= ' NULL';
            }
        }
        if (array_key_exists('default', $spec)) {
            $default = $this->escapeDefaultValue($spec['default']);
            $sql .= " default {$default}";
        }
        return $sql;
    }
    
    /**
     * Set database-engine specific properties for a field.
     *
     * @param $field
     *   A field description array, as specified in the schema documentation.
     */
    protected function processField($field) {
        if (!isset($field['size'])) {
            $field['size'] = 'normal';
        }
        // Set the correct database-engine specific datatype.
        // In case one is already provided, force it to lowercase.
        if (isset($field['pgsql_type'])) {
            $field['pgsql_type'] = mb_strtolower($field['pgsql_type']);
        }
        else {
            $map = $this->getFieldTypeMap();
            $field['pgsql_type'] = $map[$field['type'] . ':' . $field['size']];
        }
        if (!empty($field['unsigned'])) {
            // Unsigned data types are not supported in PostgreSQL 10. In MySQL,
            // they are used to ensure a positive number is inserted and it also
            // doubles the maximum integer size that can be stored in a field.
            // The PostgreSQL schema in Drupal creates a check constraint
            // to ensure that a value inserted is >= 0. To provide the extra
            // integer capacity, here, we bump up the column field size.
            if (!isset($map)) {
                $map = $this->getFieldTypeMap();
            }
            switch ($field['pgsql_type']) {
                case 'smallint':
                    $field['pgsql_type'] = $map['int:medium'];
                    break;
                case 'int':
                    $field['pgsql_type'] = $map['int:big'];
                    break;
            }
        }
        if (isset($field['type']) && $field['type'] == 'serial') {
            unset($field['not null']);
        }
        return $field;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFieldTypeMap() {
        // Put :normal last so it gets preserved by array_flip. This makes
        // it much easier for modules (such as schema.module) to map
        // database types back into schema types.
        // $map does not use drupal_static as its value never changes.
        static $map = [
            'varchar_ascii:normal' => 'varchar',
            'varchar:normal' => 'varchar',
            'char:normal' => 'character',
            'text:tiny' => 'text',
            'text:small' => 'text',
            'text:medium' => 'text',
            'text:big' => 'text',
            'text:normal' => 'text',
            'int:tiny' => 'smallint',
            'int:small' => 'smallint',
            'int:medium' => 'int',
            'int:big' => 'bigint',
            'int:normal' => 'int',
            'float:tiny' => 'real',
            'float:small' => 'real',
            'float:medium' => 'real',
            'float:big' => 'double precision',
            'float:normal' => 'real',
            'numeric:normal' => 'numeric',
            'blob:big' => 'bytea',
            'blob:normal' => 'bytea',
            'serial:tiny' => 'serial',
            'serial:small' => 'serial',
            'serial:medium' => 'serial',
            'serial:big' => 'bigserial',
            'serial:normal' => 'serial',
        ];
        return $map;
    }
    protected function _createKeySql($fields) {
        $return = [];
        foreach ($fields as $field) {
            if (is_array($field)) {
                $return[] = 'substr(' . $field[0] . ', 1, ' . $field[1] . ')';
            }
            else {
                $return[] = '"' . $field . '"';
            }
        }
        return implode(', ', $return);
    }
    
    /**
     * Create the SQL expression for primary keys.
     *
     * Postgresql does not support key length. It does support fillfactor, but
     * that requires a separate database lookup for each column in the key. The
     * key length defined in the schema is ignored.
     */
    protected function createPrimaryKeySql($fields) {
        $return = [];
        foreach ($fields as $field) {
            if (is_array($field)) {
                $return[] = '"' . $field[0] . '"';
            }
            else {
                $return[] = '"' . $field . '"';
            }
        }
        return implode(', ', $return);
    }
    
    /**
     * {@inheritdoc}
     */
    public function tableExists($table) {
        $prefixInfo = $this->getPrefixInfo($table, TRUE);
        return (bool) $this->connection
            ->query("SELECT 1 FROM pg_tables WHERE schemaname = :schema AND tablename = :table", [
            ':schema' => $prefixInfo['schema'],
            ':table' => $prefixInfo['table'],
        ])
            ->fetchField();
    }
    
    /**
     * {@inheritdoc}
     */
    public function findTables($table_expression) {
        $individually_prefixed_tables = $this->connection
            ->getUnprefixedTablesMap();
        $default_prefix = $this->connection
            ->tablePrefix();
        $default_prefix_length = strlen($default_prefix);
        $tables = [];
        // Load all the tables up front in order to take into account per-table
        // prefixes. The actual matching is done at the bottom of the method.
        $results = $this->connection
            ->query("SELECT tablename FROM pg_tables WHERE schemaname = :schema", [
            ':schema' => $this->defaultSchema,
        ]);
        foreach ($results as $table) {
            // Take into account tables that have an individual prefix.
            if (isset($individually_prefixed_tables[$table->tablename])) {
                $prefix_length = strlen($this->connection
                    ->tablePrefix($individually_prefixed_tables[$table->tablename]));
            }
            elseif ($default_prefix && substr($table->tablename, 0, $default_prefix_length) !== $default_prefix) {
                // This table name does not start the default prefix, which means that
                // it is not managed by Drupal so it should be excluded from the result.
                continue;
            }
            else {
                $prefix_length = $default_prefix_length;
            }
            // Remove the prefix from the returned tables.
            $unprefixed_table_name = substr($table->tablename, $prefix_length);
            // The pattern can match a table which is the same as the prefix. That
            // will become an empty string when we remove the prefix, which will
            // probably surprise the caller, besides not being a prefixed table. So
            // remove it.
            if (!empty($unprefixed_table_name)) {
                $tables[$unprefixed_table_name] = $unprefixed_table_name;
            }
        }
        // Convert the table expression from its SQL LIKE syntax to a regular
        // expression and escape the delimiter that will be used for matching.
        $table_expression = str_replace([
            '%',
            '_',
        ], [
            '.*?',
            '.',
        ], preg_quote($table_expression, '/'));
        $tables = preg_grep('/^' . $table_expression . '$/i', $tables);
        return $tables;
    }
    
    /**
     * {@inheritdoc}
     */
    public function renameTable($table, $new_name) {
        if (!$this->tableExists($table)) {
            throw new SchemaObjectDoesNotExistException("Cannot rename '{$table}' to '{$new_name}': table '{$table}' doesn't exist.");
        }
        if ($this->tableExists($new_name)) {
            throw new SchemaObjectExistsException("Cannot rename '{$table}' to '{$new_name}': table '{$new_name}' already exists.");
        }
        // Get the schema and tablename for the old table.
        $old_full_name = str_replace('"', '', $this->connection
            ->prefixTables('{' . $table . '}'));
        [
            $old_schema,
            $old_table_name,
        ] = strpos($old_full_name, '.') ? explode('.', $old_full_name) : [
            'public',
            $old_full_name,
        ];
        // Index names and constraint names are global in PostgreSQL, so we need to
        // rename them when renaming the table.
        $indexes = $this->connection
            ->query('SELECT indexname FROM pg_indexes WHERE schemaname = :schema AND tablename = :table', [
            ':schema' => $old_schema,
            ':table' => $old_table_name,
        ]);
        foreach ($indexes as $index) {
            // Get the index type by suffix, e.g. idx/key/pkey
            $index_type = substr($index->indexname, strrpos($index->indexname, '_') + 1);
            // If the index is already rewritten by ensureIdentifiersLength() to not
            // exceed the 63 chars limit of PostgreSQL, we need to take care of that.
            // cSpell:disable-next-line
            // Example (drupal_Gk7Su_T1jcBHVuvSPeP22_I3Ni4GrVEgTYlIYnBJkro_idx).
            if (strpos($index->indexname, 'drupal_') !== FALSE) {
                preg_match('/^drupal_(.*)_' . preg_quote($index_type) . '/', $index->indexname, $matches);
                $index_name = $matches[1];
            }
            else {
                // Make sure to remove the suffix from index names, because
                // $this->ensureIdentifiersLength() will add the suffix again and thus
                // would result in a wrong index name.
                preg_match('/^' . preg_quote($old_full_name) . '__(.*)__' . preg_quote($index_type) . '/', $index->indexname, $matches);
                $index_name = $matches[1];
            }
            $this->connection
                ->query('ALTER INDEX "' . $index->indexname . '" RENAME TO ' . $this->ensureIdentifiersLength($new_name, $index_name, $index_type) . '');
        }
        // Ensure the new table name does not include schema syntax.
        $prefixInfo = $this->getPrefixInfo($new_name);
        // Rename sequences if the table contains serial fields.
        $info = $this->queryTableInformation($table);
        if (!empty($info->serial_fields)) {
            foreach ($info->serial_fields as $field) {
                // The initial name of the sequence is generated automatically by
                // PostgreSQL when the table is created, so we need to use
                // pg_get_serial_sequence() to retrieve it.
                $old_sequence = $this->connection
                    ->query("SELECT pg_get_serial_sequence('" . $old_full_name . "', '" . $field . "')")
                    ->fetchField();
                // If the new sequence name exceeds the maximum identifier length limit,
                // it will not match the pattern that is automatically applied by
                // PostgreSQL on table creation, but that's ok because
                // pg_get_serial_sequence() will return our non-standard name on
                // subsequent table renames.
                $new_sequence = $this->ensureIdentifiersLength($new_name, $field, 'seq', '_');
                $this->connection
                    ->query('ALTER SEQUENCE ' . $old_sequence . ' RENAME TO ' . $new_sequence);
            }
        }
        // Now rename the table.
        $this->connection
            ->query('ALTER TABLE {' . $table . '} RENAME TO ' . $prefixInfo['table']);
        $this->resetTableInformation($table);
    }
    
    /**
     * {@inheritdoc}
     */
    public function dropTable($table) {
        if (!$this->tableExists($table)) {
            return FALSE;
        }
        $this->connection
            ->query('DROP TABLE {' . $table . '}');
        $this->resetTableInformation($table);
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function addField($table, $field, $spec, $new_keys = []) {
        if (!$this->tableExists($table)) {
            throw new SchemaObjectDoesNotExistException("Cannot add field '{$table}.{$field}': table doesn't exist.");
        }
        if ($this->fieldExists($table, $field)) {
            throw new SchemaObjectExistsException("Cannot add field '{$table}.{$field}': field already exists.");
        }
        // Fields that are part of a PRIMARY KEY must be added as NOT NULL.
        $is_primary_key = isset($new_keys['primary key']) && in_array($field, $new_keys['primary key'], TRUE);
        if ($is_primary_key) {
            $this->ensureNotNullPrimaryKey($new_keys['primary key'], [
                $field => $spec,
            ]);
        }
        $fixnull = FALSE;
        if (!empty($spec['not null']) && !isset($spec['default']) && !$is_primary_key) {
            $fixnull = TRUE;
            $spec['not null'] = FALSE;
        }
        $query = 'ALTER TABLE {' . $table . '} ADD COLUMN ';
        $query .= $this->createFieldSql($field, $this->processField($spec));
        $this->connection
            ->query($query);
        if (isset($spec['initial_from_field'])) {
            if (isset($spec['initial'])) {
                $expression = 'COALESCE(' . $spec['initial_from_field'] . ', :default_initial_value)';
                $arguments = [
                    ':default_initial_value' => $spec['initial'],
                ];
            }
            else {
                $expression = $spec['initial_from_field'];
                $arguments = [];
            }
            $this->connection
                ->update($table)
                ->expression($field, $expression, $arguments)
                ->execute();
        }
        elseif (isset($spec['initial'])) {
            $this->connection
                ->update($table)
                ->fields([
                $field => $spec['initial'],
            ])
                ->execute();
        }
        if ($fixnull) {
            $this->connection
                ->query("ALTER TABLE {" . $table . "} ALTER {$field} SET NOT NULL");
        }
        if (isset($new_keys)) {
            // Make sure to drop the existing primary key before adding a new one.
            // This is only needed when adding a field because this method, unlike
            // changeField(), is supposed to handle primary keys automatically.
            if (isset($new_keys['primary key']) && $this->constraintExists($table, 'pkey')) {
                $this->dropPrimaryKey($table);
            }
            $this->_createKeys($table, $new_keys);
        }
        // Add column comment.
        if (!empty($spec['description'])) {
            $this->connection
                ->query('COMMENT ON COLUMN {' . $table . '}.' . $field . ' IS ' . $this->prepareComment($spec['description']));
        }
        $this->resetTableInformation($table);
    }
    
    /**
     * {@inheritdoc}
     */
    public function dropField($table, $field) {
        if (!$this->fieldExists($table, $field)) {
            return FALSE;
        }
        $this->connection
            ->query('ALTER TABLE {' . $table . '} DROP COLUMN "' . $field . '"');
        $this->resetTableInformation($table);
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function fieldExists($table, $column) {
        $prefixInfo = $this->getPrefixInfo($table);
        return (bool) $this->connection
            ->query("SELECT 1 FROM pg_attribute WHERE attrelid = :key::regclass AND attname = :column AND NOT attisdropped AND attnum > 0", [
            ':key' => $prefixInfo['schema'] . '.' . $prefixInfo['table'],
            ':column' => $column,
        ])
            ->fetchField();
    }
    
    /**
     * {@inheritdoc}
     */
    public function indexExists($table, $name) {
        // Details https://www.postgresql.org/docs/10/view-pg-indexes.html
        $index_name = $this->ensureIdentifiersLength($table, $name, 'idx');
        // Remove leading and trailing quotes because the index name is in a WHERE
        // clause and not used as an identifier.
        $index_name = str_replace('"', '', $index_name);
        return (bool) $this->connection
            ->query("SELECT 1 FROM pg_indexes WHERE indexname = '{$index_name}'")
            ->fetchField();
    }
    
    /**
     * Helper function: check if a constraint (PK, FK, UK) exists.
     *
     * @param string $table
     *   The name of the table.
     * @param string $name
     *   The name of the constraint (typically 'pkey' or '[constraint]__key').
     *
     * @return bool
     *   TRUE if the constraint exists, FALSE otherwise.
     */
    public function constraintExists($table, $name) {
        // ::ensureIdentifiersLength() expects three parameters, although not
        // explicitly stated in its signature, thus we split our constraint name in
        // a proper name and a suffix.
        if ($name == 'pkey') {
            $suffix = $name;
            $name = '';
        }
        else {
            $pos = strrpos($name, '__');
            $suffix = substr($name, $pos + 2);
            $name = substr($name, 0, $pos);
        }
        $constraint_name = $this->ensureIdentifiersLength($table, $name, $suffix);
        // Remove leading and trailing quotes because the index name is in a WHERE
        // clause and not used as an identifier.
        $constraint_name = str_replace('"', '', $constraint_name);
        return (bool) $this->connection
            ->query("SELECT 1 FROM pg_constraint WHERE conname = '{$constraint_name}'")
            ->fetchField();
    }
    
    /**
     * {@inheritdoc}
     */
    public function addPrimaryKey($table, $fields) {
        if (!$this->tableExists($table)) {
            throw new SchemaObjectDoesNotExistException("Cannot add primary key to table '{$table}': table doesn't exist.");
        }
        if ($this->constraintExists($table, 'pkey')) {
            throw new SchemaObjectExistsException("Cannot add primary key to table '{$table}': primary key already exists.");
        }
        $this->connection
            ->query('ALTER TABLE {' . $table . '} ADD CONSTRAINT ' . $this->ensureIdentifiersLength($table, '', 'pkey') . ' PRIMARY KEY (' . $this->createPrimaryKeySql($fields) . ')');
        $this->resetTableInformation($table);
    }
    
    /**
     * {@inheritdoc}
     */
    public function dropPrimaryKey($table) {
        if (!$this->constraintExists($table, 'pkey')) {
            return FALSE;
        }
        $this->connection
            ->query('ALTER TABLE {' . $table . '} DROP CONSTRAINT ' . $this->ensureIdentifiersLength($table, '', 'pkey'));
        $this->resetTableInformation($table);
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function findPrimaryKeyColumns($table) {
        if (!$this->tableExists($table)) {
            return FALSE;
        }
        return $this->connection
            ->query("SELECT array_position(i.indkey, a.attnum) AS position, a.attname FROM pg_index i JOIN pg_attribute a ON a.attrelid = i.indrelid AND a.attnum = ANY(i.indkey) WHERE i.indrelid = '{" . $table . "}'::regclass AND i.indisprimary ORDER BY position")
            ->fetchAllKeyed();
    }
    
    /**
     * {@inheritdoc}
     */
    public function addUniqueKey($table, $name, $fields) {
        if (!$this->tableExists($table)) {
            throw new SchemaObjectDoesNotExistException("Cannot add unique key '{$name}' to table '{$table}': table doesn't exist.");
        }
        if ($this->constraintExists($table, $name . '__key')) {
            throw new SchemaObjectExistsException("Cannot add unique key '{$name}' to table '{$table}': unique key already exists.");
        }
        $this->connection
            ->query('ALTER TABLE {' . $table . '} ADD CONSTRAINT ' . $this->ensureIdentifiersLength($table, $name, 'key') . ' UNIQUE (' . implode(',', $fields) . ')');
        $this->resetTableInformation($table);
    }
    
    /**
     * {@inheritdoc}
     */
    public function dropUniqueKey($table, $name) {
        if (!$this->constraintExists($table, $name . '__key')) {
            return FALSE;
        }
        $this->connection
            ->query('ALTER TABLE {' . $table . '} DROP CONSTRAINT ' . $this->ensureIdentifiersLength($table, $name, 'key'));
        $this->resetTableInformation($table);
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function addIndex($table, $name, $fields, array $spec) {
        if (!$this->tableExists($table)) {
            throw new SchemaObjectDoesNotExistException("Cannot add index '{$name}' to table '{$table}': table doesn't exist.");
        }
        if ($this->indexExists($table, $name)) {
            throw new SchemaObjectExistsException("Cannot add index '{$name}' to table '{$table}': index already exists.");
        }
        $this->connection
            ->query($this->_createIndexSql($table, $name, $fields));
        $this->resetTableInformation($table);
    }
    
    /**
     * {@inheritdoc}
     */
    public function dropIndex($table, $name) {
        if (!$this->indexExists($table, $name)) {
            return FALSE;
        }
        $this->connection
            ->query('DROP INDEX ' . $this->ensureIdentifiersLength($table, $name, 'idx'));
        $this->resetTableInformation($table);
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function introspectIndexSchema($table) {
        if (!$this->tableExists($table)) {
            throw new SchemaObjectDoesNotExistException("The table {$table} doesn't exist.");
        }
        $index_schema = [
            'primary key' => [],
            'unique keys' => [],
            'indexes' => [],
        ];
        // Get the schema and tablename for the table without identifier quotes.
        $full_name = str_replace('"', '', $this->connection
            ->prefixTables('{' . $table . '}'));
        $result = $this->connection
            ->query("SELECT i.relname AS index_name, a.attname AS column_name FROM pg_class t, pg_class i, pg_index ix, pg_attribute a WHERE t.oid = ix.indrelid AND i.oid = ix.indexrelid AND a.attrelid = t.oid AND a.attnum = ANY(ix.indkey) AND t.relkind = 'r' AND t.relname = :table_name ORDER BY index_name ASC, column_name ASC", [
            ':table_name' => $full_name,
        ])
            ->fetchAll();
        foreach ($result as $row) {
            if (preg_match('/_pkey$/', $row->index_name)) {
                $index_schema['primary key'][] = $row->column_name;
            }
            elseif (preg_match('/_key$/', $row->index_name)) {
                $index_schema['unique keys'][$row->index_name][] = $row->column_name;
            }
            elseif (preg_match('/_idx$/', $row->index_name)) {
                $index_schema['indexes'][$row->index_name][] = $row->column_name;
            }
        }
        return $index_schema;
    }
    
    /**
     * {@inheritdoc}
     */
    public function changeField($table, $field, $field_new, $spec, $new_keys = []) {
        if (!$this->fieldExists($table, $field)) {
            throw new SchemaObjectDoesNotExistException("Cannot change the definition of field '{$table}.{$field}': field doesn't exist.");
        }
        if ($field != $field_new && $this->fieldExists($table, $field_new)) {
            throw new SchemaObjectExistsException("Cannot rename field '{$table}.{$field}' to '{$field_new}': target field already exists.");
        }
        if (isset($new_keys['primary key']) && in_array($field_new, $new_keys['primary key'], TRUE)) {
            $this->ensureNotNullPrimaryKey($new_keys['primary key'], [
                $field_new => $spec,
            ]);
        }
        $spec = $this->processField($spec);
        // Type 'serial' is known to PostgreSQL, but only during table creation,
        // not when altering. Because of that, we create it here as an 'int'. After
        // we create it we manually re-apply the sequence.
        if (in_array($spec['pgsql_type'], [
            'serial',
            'bigserial',
        ])) {
            $field_def = 'int';
        }
        else {
            $field_def = $spec['pgsql_type'];
        }
        if (in_array($spec['pgsql_type'], [
            'varchar',
            'character',
            'text',
        ]) && isset($spec['length'])) {
            $field_def .= '(' . $spec['length'] . ')';
        }
        elseif (isset($spec['precision']) && isset($spec['scale'])) {
            $field_def .= '(' . $spec['precision'] . ', ' . $spec['scale'] . ')';
        }
        // Remove old check constraints.
        $field_info = $this->queryFieldInformation($table, $field);
        foreach ($field_info as $check) {
            $this->connection
                ->query('ALTER TABLE {' . $table . '} DROP CONSTRAINT "' . $check . '"');
        }
        // Remove old default.
        $this->connection
            ->query('ALTER TABLE {' . $table . '} ALTER COLUMN "' . $field . '" DROP DEFAULT');
        // Convert field type.
        // Usually, we do this via a simple typecast 'USING fieldname::type'. But
        // the typecast does not work for conversions to bytea.
        // @see http://www.postgresql.org/docs/current/static/datatype-binary.html
        $table_information = $this->queryTableInformation($table);
        $is_bytea = !empty($table_information->blob_fields[$field]);
        if ($spec['pgsql_type'] != 'bytea') {
            if ($is_bytea) {
                $this->connection
                    ->query('ALTER TABLE {' . $table . '} ALTER "' . $field . '" TYPE ' . $field_def . ' USING convert_from("' . $field . '"' . ", 'UTF8')");
            }
            else {
                $this->connection
                    ->query('ALTER TABLE {' . $table . '} ALTER "' . $field . '" TYPE ' . $field_def . ' USING "' . $field . '"::' . $field_def);
            }
        }
        else {
            // Do not attempt to convert a field that is bytea already.
            if (!$is_bytea) {
                // Convert to a bytea type by using the SQL replace() function to
                // convert any single backslashes in the field content to double
                // backslashes ('\' to '\\').
                $this->connection
                    ->query('ALTER TABLE {' . $table . '} ALTER "' . $field . '" TYPE ' . $field_def . ' USING decode(replace("' . $field . '"' . ", E'\\\\', E'\\\\\\\\'), 'escape');");
            }
        }
        if (isset($spec['not null'])) {
            if ($spec['not null']) {
                $null_action = 'SET NOT NULL';
            }
            else {
                $null_action = 'DROP NOT NULL';
            }
            $this->connection
                ->query('ALTER TABLE {' . $table . '} ALTER "' . $field . '" ' . $null_action);
        }
        if (in_array($spec['pgsql_type'], [
            'serial',
            'bigserial',
        ])) {
            // Type "serial" is known to PostgreSQL, but *only* during table creation,
            // not when altering. Because of that, the sequence needs to be created
            // and initialized by hand.
            $seq = $this->connection
                ->makeSequenceName($table, $field_new);
            $this->connection
                ->query("CREATE SEQUENCE " . $seq);
            // Set sequence to maximal field value to not conflict with existing
            // entries.
            $this->connection
                ->query("SELECT setval('" . $seq . "', MAX(\"" . $field . '")) FROM {' . $table . "}");
            $this->connection
                ->query('ALTER TABLE {' . $table . '} ALTER ' . $field . ' SET DEFAULT nextval(' . $this->connection
                ->quote($seq) . ')');
        }
        // Rename the column if necessary.
        if ($field != $field_new) {
            $this->connection
                ->query('ALTER TABLE {' . $table . '} RENAME "' . $field . '" TO "' . $field_new . '"');
        }
        // Add unsigned check if necessary.
        if (!empty($spec['unsigned'])) {
            $this->connection
                ->query('ALTER TABLE {' . $table . '} ADD CHECK ("' . $field_new . '" >= 0)');
        }
        // Add default if necessary.
        if (isset($spec['default'])) {
            $this->connection
                ->query('ALTER TABLE {' . $table . '} ALTER COLUMN "' . $field_new . '" SET DEFAULT ' . $this->escapeDefaultValue($spec['default']));
        }
        // Change description if necessary.
        if (!empty($spec['description'])) {
            $this->connection
                ->query('COMMENT ON COLUMN {' . $table . '}."' . $field_new . '" IS ' . $this->prepareComment($spec['description']));
        }
        if (isset($new_keys)) {
            $this->_createKeys($table, $new_keys);
        }
        $this->resetTableInformation($table);
    }
    protected function _createIndexSql($table, $name, $fields) {
        $query = 'CREATE INDEX ' . $this->ensureIdentifiersLength($table, $name, 'idx') . ' ON {' . $table . '} (';
        $query .= $this->_createKeySql($fields) . ')';
        return $query;
    }
    protected function _createKeys($table, $new_keys) {
        if (isset($new_keys['primary key'])) {
            $this->addPrimaryKey($table, $new_keys['primary key']);
        }
        if (isset($new_keys['unique keys'])) {
            foreach ($new_keys['unique keys'] as $name => $fields) {
                $this->addUniqueKey($table, $name, $fields);
            }
        }
        if (isset($new_keys['indexes'])) {
            foreach ($new_keys['indexes'] as $name => $fields) {
                // Even though $new_keys is not a full schema it still has 'indexes' and
                // so is a partial schema. Technically addIndex() doesn't do anything
                // with it so passing an empty array would work as well.
                $this->addIndex($table, $name, $fields, $new_keys);
            }
        }
    }
    
    /**
     * Retrieve a table or column comment.
     */
    public function getComment($table, $column = NULL) {
        $info = $this->getPrefixInfo($table);
        // Don't use {} around pg_class, pg_attribute tables.
        if (isset($column)) {
            return $this->connection
                ->query('SELECT col_description(oid, attnum) FROM pg_class, pg_attribute WHERE attrelid = oid AND relname = ? AND attname = ?', [
                $info['table'],
                $column,
            ])
                ->fetchField();
        }
        else {
            return $this->connection
                ->query('SELECT obj_description(oid, ?) FROM pg_class WHERE relname = ?', [
                'pg_class',
                $info['table'],
            ])
                ->fetchField();
        }
    }
    
    /**
     * Calculates a base-64 encoded PostgreSQL-safe sha-256 hash.
     *
     * The hash is modified to according to  @link https://www.postgresql.org/docs/current/sql-syntax-lexical.html PostgreSQL Lexical Structure@endlink.
     *
     * @param $data
     *   String to be hashed.
     *
     * @return string
     *   A base-64 encoded sha-256 hash, with + and / replaced with _ and any =
     *   padding characters removed.
     */
    protected function hashBase64($data) {
        $hash = base64_encode(hash('sha256', $data, TRUE));
        // Modify the hash so it's safe to use in PostgreSQL identifiers.
        return strtr($hash, [
            '+' => '_',
            '/' => '_',
            '=' => '',
        ]);
    }
    
    /**
     * Determines whether the PostgreSQL extension is created.
     *
     * @param string $name
     *   The name of the extension.
     *
     * @return bool
     *   Return TRUE when the extension is created, FALSE otherwise.
     *
     * @internal
     */
    public function extensionExists($name) : bool {
        return (bool) $this->connection
            ->query('SELECT installed_version FROM pg_available_extensions WHERE name = :name', [
            ':name' => $name,
        ])
            ->fetchField();
    }

}